The effects of phototoxic agents such as anthracene and derivatives of crude coal tar will be combined with various wavelengths of ultraviolet light to determine the effect on DNA synthesis in the epidermis of hairless mice. Retinoids will be examined for their topical and systemic effect on ornithine decarboxylase activity in the skin of hairless mice. New techniques to grow the epidermal cells of newborn hairless mice in culture will be tested. A skin disc technique for measuring DNA synthesis in hairless mice will be investigated thoroughly with regard to reliability and simplification so that it can be substituted for the previous hydroxylapatite extraction techniques for measuring DNA synthesis in the epidermal cells.